Methods for the purification of human prolactin from amniotic fluid will be refined. Studies on the physiology and clinical significance of human prolactin will be continued. The purification and chemical characterization of placental lactogens from sheep, cow, goat and rats will be undertaken. The biological effects of these placental hormones will be investigated. Studies on plasma membrane receptors for prolactin, growth hormone and insulin will be continued. In particular, the purfication and characterization of rabbit mammary gland receptors for prolactin and rabbit liver receptors for growth hormone will be attempted.